1. Field of the Invention
The present invention relates generally to mobile communication networks and specifically to use of overhead messages within mobile communication networks. Still more particularly, the present invention relates to a method, system, and mobile communications network that enable a single overhead message component to include multiple band-class records that are utilized by mobile stations to individually select a frequency for operation.
2. Description of the Related Art
As mobile communication technology improves, CDMA communication standards and systems have evolved from IS-95A and IS-95B systems to more modern IS-2000 communication systems. Mobile communication devices (e.g., base stations (BS) and mobile stations (MS)) may be designed to support one or more of these standards, and it is common for legacy devices (e.g., IS-95A MS) to be supported by the newer/more modern standards (i.e., IS-2000). Support for a particular standard is typically defined by providing the device with a particular protocol revision (P_Rev) value. For example, a protocol revision value for the IS-95A service may be 2 (range 0-2), a protocol revision value for the IS-95B standard may be 5 (range 3 to 5), and a protocol revision value for the IS-2000 standard may be 6 (or range 6+).
Conventional Code Division Multiple Access (CDMA) wireless/mobile communication systems comprise mobile switching centers (MSC) and base stations (BS) that transmit/communicate control information to mobile stations (MS) via various types of overhead messages. Conventional overhead messages are sent by a base station to all mobile stations to establish system operating parameters by communicating information that may be specific to the base station or may be common to the entire system. For example, the BS of a mobile communication system typically also supports a plurality of frequency assignments. To inform a mobile station (e.g., cellular telephone) of the supported frequencies, the BS generates and sends to the MS a CDMA channel list message (CCLM) for IS-95A operation or an extended CDMA channel list message (ECCLM) for IS-2000 operation. Generally speaking, only one or the other of the CCLM and ECCLM is received by a mobile station at any given time, since IS-95A and IS-95B configured base systems only send out a CCLM while IS-2000 base systems only send out an ECCLM. Both message-types are overhead messages sent out over a forward paging channel or a forward broadcast control channel.
In addition to the above messages, the TIA/EIA (Telecommunications Industry Association/Electronic Industries Association) IS-2000 standard provides an Extended Channel Assignment Message (ECAM) that includes the capability for a communication system to assign a mobile station (MS) to a paging channel or a traffic channel in a different, alternate frequency band class than a frequency band class initially accessed by the MS. Additionally, in conventional network communication systems that support multiple band classes, the BS is able to utilize service redirection messages to redirect mobile stations to different band classes. One such redirection message in the IS-2000 standard is the (Extended) Global Service Redirection Message (EGSRDM). EGSRDM is a broadcast-type message, and conventional EGSRDM structure only allows one band class record to be provided within the single message to redirect a group of mobile stations to the band class. When an EGSRDM is utilized, each MS that meets the requirements for redirection will be redirected to the new band class specified in the message. In some implementations, after the mobile station moves to the new band class, the BS may transmit an ECCLM that may move the mobile station(s) to a different frequency supported within that band class. In current CDMA system, a BS may perform some balancing of the system load by redirecting some mobiles to other supported frequencies within the same band class.
Conventional EGSRDM are able to specify only one redirection record (corresponding to a single band class), although current communications systems typically support multiple band classes. Given this limitation, the current EGSRDM structure is thus incapable of efficiently directing different groups of MSs to different band classes when multiple band classes are supported in the system. That is a single EGSRDM is not able to redirect different groups of mobile devices to multiple band classes and the BS is made to complete. Redirection of different groups necessarily requires the BS issue multiple EGSRDMs (overhead messages) with each message having a different redirection record included therein. Such a process leads to (a) congestion/cluttering of the network (or control channels) with these multiple broadcasts and (b) also forces all mobile devices to continually update the overhead messages, leading to greater power consumption by the devices.
Further, due to the capacity limitation of some legacy mobiles, some networks are forced to direct all mobiles (with any MOB_P_REV revision) to the same frequency that only supports legacy channels (e.g., Paging Channel). The BS then uses EGSRDM to redirect all mobiles that supports new common channel types (e.g., BCCH) to the frequency that support the new common channel types. Since with current EGSRDMs, the BS is only allowed to include one redirection record in a message to redirect a group of mobile stations to a single band class, if a network supports multiple band classes, the BS must first utilize an EGSRDM to redirect a group of mobiles to a frequency on different band class or to a frequency on the same band class that support different type of common channel. The frequency allocation may then be provided by the BS transmitting an ECCLM to distribute mobiles to different frequencies on that band. However, when there are multiple groups of mobiles, with each group having different system selection criteria (i.e., supporting different bands), the use of conventional EGSRDM methods does not allow the BS to simultaneously redirect each of these different groups of mobile devices with a single overhead message. That is, use of a single EGSRDM with its single redirection record is typically not flexible enough for an operator to effectively balance the existing load, when the BS and MS support multiple band classes.
The following summarizes several of the limitations/issues found with current EGSRDM structure:                (1) EGSRDM has only been available since IS-2000 Rel 0, and Rev 0 mobile device(s) does not support Rev A common channels (e.g. BCCH). The BS is unable to utilize single EGSRDM to direct IS-95 and Rev 0 mobile device(s) to a Paging Channel and Rev A mobile device(s) to Rev A new common channels (e.g., BCCH);        (2) If two (or more) band classes are available in the system, and both band classes supports PCH and BCCH, the BS is unable to efficiently distribute Rev 0 mobile device(s) and post Rev 0 mobile device(s) among all the supported band classes with one redirection record; and        (3) While the BS is able to utilize EGSRDM to redirect all the post Rev 0 mobile device(s) to a frequency that supports new common channels, if multiple band classes are supported, the BS needs to send another EGSRDM to redirect some post Rev 0 mobile device(s) to a different band class. This process requires at least two EGSRDMs to move mobile device(s) to multiple different band classes. If Rev 0 mobiles represent the majority of mobile stations in the system, the BS needs to send multiple EGSRDMs, each targeting a different group of mobile stations in order to achieve load balance among all the supported band classes. This process will force all mobile devices to perform multiple rounds of overhead message updates, which negatively impact mobile performance.        